1. Field of the Invention
The present invention relates to an electric power steering apparatus.
2. Description of the Related Art
As shown in a Japanese unexamined Patent Publication No. (JP-A) 8-34355, an electric power steering apparatus is structured such that a pinion shaft connected to a steering shaft is engaged with a rack shaft. A worm gear is provided in a drive shaft connected to an electric motor and a worm wheel engaged with the worm gear is connected to the pinion shaft, whereby a torque of the motor is transmitted to the rack shaft so as to assist a steering operation.
In an electric power steering apparatus, one type of lubricating material or grease is used for an engagement portion between the pinion shaft and the rack shaft, and another type of lubricating material or grease is used for an engagement portion between the worm gear and the worm wheel. The two engagement portions mentioned above are arranged within a housing which forms the same space, and the engagement portion between the worm gear and the worm wheel is positioned above the engagement portion between the pinion shaft and the rack shaft. Accordingly, in the conventional art, the lubricating material in the engagement portion between the worm gear and the worm wheel flows down to a lower engagement portion between the pinion shaft and the rack shaft so as to be mixed with the lubricating material in the engagement portion between the pinion shaft and the rack shaft. This generates an unexpected change in the nature of the grease to be used for the engagement portion between the pinion shaft and the rack shaft and causes a reduction of durability due to an inferior lubrication between the pinion shaft and the rack shaft.
An object of the present invention is to improve lubricating performance between a pinion shaft and a rack shaft and improve a durability thereof at while simultaneously providing both engagement portion between the pinion shaft and the rack shaft and engagement portion between a drive gear and an intermediate gear in the same space formed by a housing, in an electric power steering apparatus.
In accordance with the present invention, there is provided an electric power steering apparatus comprising:
a pinion shaft connected to a steering shaft, the pinion shaft being inserted to an inner portion of a housing so as to be engaged with a rack shaft.
A drive gear is provided, connected to an electric motor, and an intermediate gear connected to the pinion shaft, the drive gear and the intermediate gear being engaged with each other in an upper portion of an engagement portion between the pinion shaft and the rack shaft disposed within the housing.
Storage for the lubricating material is provided in a lower portion of the engagement portion between the drive gear and the intermediate gear in the housing. A partition wall prevents the lubricating material from dripping down from the storage area to an area where the engagement portion between the pinion shaft and the rack shaft is provided in a periphery of a portion through which the pinion shaft of the housing is inserted.